US 9,752,710 B2 · Assignee: NIPPON STEEL & SUMITOMO METAL CORPORATION · Inventors: Goto; Kunio et al.
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A tubular threaded joint is constituted by a pin and a box each having a contact surface comprising an unthreaded metal contact portion including a seal portion and a shoulder portion and a threaded portion. Of the contact surface of at least one of the pin and the box, the surfaces of the seal portion and the shoulder portion has a first lubricating coating in the form of a solid lubricating coating, and the surface of the threaded portion or the entire surface of the contact surface has a second lubricating coating selected from a viscous liquid lubricating coating and a solid lubricating coating. The first lubricating coating has a coefficient of friction which is higher than that of the second lubricating coating, and the second lubricating coating is positioned on top in a portion where both the first lubricating coating and the second lubricating coating are present.
Oil country tubular goods such as tubing and casing used for excavation of oil wells for exploitation of crude oil or gas oil are usually connected with each other (made up) using tubular threaded joints. In the past, the depth of oil wells was 2,000-3,000 meters, but in deep wells such as recent oil fields in the sea, the depth sometimes reaches 8,000-10,000 meters or larger. The length of oil country tubular goods is typically 10 some meters, and tubing through which a fluid such as crude oil flows is surrounded by a plurality of casings. Therefore, the number of oil country tubular goods which are connected by threaded joints reaches a huge number. Since tubular threaded joints for oil country tubular goods are subjected in their environment of use to loads in the than of tensile forces in the axial direction caused by the mass of oil country tubular goods and the joints themselves, c
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This invention relates to a tubular threaded joint used for connecting steel pipes and particularly oil country tubular goods and to a surface treatment method therefor. A tubular threaded joint according to the present invention can reliably exhibit excellent galling resistance without the application of a lubricating grease such as compound grease which in the past has been applied to threaded joints each time when makeup of oil country tubular goods is carried out. Therefore, a tubular threaded joint according to the present invention can avoid the adverse effects on the global environment and humans caused by compound grease. In addition, the joint does not readily yield even if makeup is carried out with a high torque, thereby making it possible to realize a stable metal-to-metal seal with an adequate operating margin.
Oil country tubular goods such as tubing and casing used for excavation of oil wells for exploitation of crude oil or gas oil are usually connected with each other (made up) using tubular threaded joints. In the past, the depth of oil wells was 2,000-3,000 meters, but in deep wells such as recent oil fields in the sea, the depth sometimes reaches 8,000-10,000 meters or larger. The length of oil country tubular goods is typically 10 some meters, and tubing through which a fluid such as crude oil flows is surrounded by a plurality of casings. Therefore, the number of oil country tubular goods which are connected by threaded joints reaches a huge number.
Since tubular threaded joints for oil country tubular goods are subjected in their environment of use to loads in the than of tensile forces in the axial direction caused by the mass of oil country tubular goods and the joints themselves, compound pressures such as internal and external pressures, and geothermal heat, they need to maintain gas tightness without being damaged even in such severe environments.
Typical tubular threaded joints used for connecting oil country tubular goods (also referred to as special threaded joints) have a pin-box structure. A pin, which is a joint component having male (external) threads, is typically formed on the outer surface of both ends of an oil country tubular good, and a box, which is a counterpart joint component having female (internal) threads which engage with the male threads, is typically formed on the inner surface of both sides of a coupling, which is a separate member. As shown in FIG. 1 , the pin has a shoulder portion (also referred to as a torque shoulder) formed on the end surface at the tip of the pin and a seal portion formed between the end surface and the male threads. Correspondingly, the box has a seal portion and a shoulder portion located in the rear of the female threads and adapted to contact the seal portion and the shoulder portion of the pin, respectively. The seal portions and the shoulder portions of the pin and the box constitute unthreaded metal contact portions of a tubular threaded joint, and the unthreaded metal contact portions and the threaded portions of the pin and the box constitute contact surfaces of a tubular threaded joint. Below-described Patent Document 1 discloses an example of such a special threaded joint.
In order to perform makeup of this tubular threaded joint, one end (the pin) of an oil country tubular good is inserted into a coupling (box), and the male threads and the female threads are tightened until the shoulder portions of the pin and the box contact each other and interfere with a suitable torque. As a result, the seal portions of the pin and the box intimately contact each other to form a metal-to-metal seal which guarantees the gas tightness of the threaded joint.
Due to various troubles occurring during the process of lowering tubing or casing into an oil well, it is sometimes necessary to loosen a threaded joint which has been made up, raise the joint from the oil well, retighten it, and again lower it into the well. API (American Petroleum Institute) requires galling resistance such that unrepairable seizing referred to as galling does not take place and gas tightness is maintained even if tightening (makeup) and loosening (breakout) are carried out 10 times on a joint for tubing and 3 times on a joint for casing.
In order to increase galling resistance and gas tightness, a viscous liquid lubricant (lubricating grease) referred to as compound grease or dope and containing heavy metal powder has been previously applied to the contact surfaces of a threaded joint each time makeup is carried out. Such compound grease is prescribed by API BUL 5A2.
With the object of increasing the retention of compound grease and improving sliding properties, it has been proposed to subject the contact surfaces of a threaded joint to various types of surface treatment to form one or more layers such as nitride treatment, various types of plating including galvanizing and dispersion plating, and phosphate chemical conversion treatment. However, as stated below, the use of compound grease may have adverse effects on the environment and humans.
Compound grease contains large amounts of powder of heavy metals such as zinc, lead, and copper. At the time of makeup of a threaded joint, the applied grease is washed off or overflows to the outer surface, and it can have an adverse effect on the environment and especially on sea life particularly due to harmful heavy metals such as lead. In addition, the process of applying compound grease worsens the work environment and the work efficiency, and there is also a concern of harm to humans.
In recent years, as a result of the enactment in 1998 of the OSPAR Convention (Oslo-Paris Convention) aimed at preventing marine pollution in the Northeast Atlantic, strict environmental regulations are being enacted on a global scale, and in some regions, the use of compound grease is already being regulated. Accordingly, in order to avoid harmful effects on the environment and humans during the excavation of gas wells and oil wells, a demand has developed for threaded joints which can exhibit excellent galling resistance without using compound grease.
As a threaded joint which can be used to connect oil country tubular goods without application of compound grease, the present applicant proposed in Patent Document 2 a threaded joint for steel pipes having a viscous liquid or semisolid lubricating coating and in Patent Document 3 a threaded joint for steel pipes having a solid lubricating coating. Patent Document 1: JP 5-87275 A Patent Document 2: JP 2002-173692 A Patent Document 3:
As stated above, with a special threaded joint like that shown in FIG. 1 constituted by a pin and a box each with a seal portion, the seal portions of the pin and the box form a metal-to-metal seal to guarantee gas tightness at the end of makeup.
FIG. 2 shows a torque chart at the time of makeup of this type of threaded joint (ordinate: torque, abscissa: number of turns). As shown in this figure, as rotation takes place, the threaded portions of the pin and the box initially contact and torque gradually increases. Subsequently, the seal portions of the pin and the box contact, and the rate of increase of torque increases. Eventually, the shoulder portion at the tip of the pin and the shoulder portion of the box contact and begin to interfere (the torque at the start of this interference is referred to as the shouldering torque Ts), upon which the torque abruptly increases. Makeup is completed when the torque reaches a predetermined makeup torque. The optimum torque in FIG. 2 means the torque that is optimal for the completion of makeup with achieving an amount of interference in the seal portions which is necessary for guaranteeing gas is tightness. A proper value for the optimum torque is predetermined depending on the internal diameter and the type of a joint.
However, in a special threaded joint used in very deep wells in which compressive stresses and bending stresses are applied, makeup is sometimes carried out with a torque which is higher than usual to prevent the tightened thread from loosening. In this case, the shoulder portion at the end of the pin and the shoulder portion of the box which it contacts sometimes yield, leading to plastic deformation of the shoulder portion of at least one member of the pin and the box. As a result, as shown in FIG. 2 , the rate of increase of torque suddenly decreases. The torque at the time when yielding and plastic deformation occur is referred to as the yield torque Ty. Yielding of the shoulder portions leads to a failure of gas tightness.
In a threaded joint which is made up with a high torque, it is advantageous for the value of [Ty minus Ts] (Ty−Ts=ΔT, or the torque-on-shoulder resistance) to be large. However, in the tubular threaded joints described in Patent Document 2 having a viscous liquid or semisolid lubricating coating, Ty is low compared to when a conventional compound grease is applied. As a result, ΔT becomes small, and the shoulder portions yield at a low makeup torque, so it is sometimes impossible to perform makeup with a high torque. In the tubular threaded joints described in Patent Document 3 having a solid lubricating coating as well, ΔT becomes smaller than that of a conventional compound grease.
The object of the present invention is to provide a tubular threaded joint which does not readily undergo yielding of its shoulder portions even when it is made up with a high torque and which has a lubricating coating which does not contain harmful heavy metals, which has excellent galling resistance, gas tightness, and rust-preventing properties, and which can afford a large ΔT to the joint.
It was found that even if the composition of a lubricating coating is varied so as to vary its coefficient of friction, ΔT does not greatly change because Ts and Ty typically vary in the same direction. For example, if the coefficient of friction of a lubricating coating increases, Ty increases, but Ts also increases (a phenomenon referred to as high shouldering). As a result, in the worst case, the condition referred to as no-shouldering occurs in which the shoulder portions do not contact at a predetermined makeup torque and makeup cannot be completed.
The present inventors found that with a tubular threaded joint having a viscous liquid or solid lubricating coating which does not contain harmful heavy metals which impose a burden on the global environment, by forming a high-friction solid lubricating coating on a portion of the contact surface (the threaded portion and the unthreaded metal contact portion) of at least one of a pin and a box such as on the shoulder portion which is initially contacted and preferably on the unthreaded metal contact portion including the seal portion and the shoulder portion, and forming on at least the remaining portion of the contact surface a lubricating coating selected from a viscous liquid lubricating coating and a solid lubricating coating having a lower coefficient of friction than the high-friction solid lubricating coating, a tubular threaded joint is obtained which has a large ΔT and which does not undergo no-shouldering while having sufficient galling resistance, gas tightness, and rust-preventing properties.
The mechanism by which a large ΔT is achieved is thought to be generally as follows.
Makeup of a tubular threaded joint is carried out by inserting a pin into a box and then rotating the pin or the box. Initially only the threaded portions of the pin and the box contact and threadingly engage with each other. In the final stage of makeup, the seal portions and the shoulder portions begin to contact, and makeup is completed when a predetermined amount of interference is obtained between the seal portions and the shoulder portions.
As shown in FIG. 5(A) , for example, with a tubular threaded joint having a high-friction solid lubricating coating on the seal portions and the shoulder portions of the contact surfaces of both a pin and a box and a lubricating coating having a lower coefficient of friction on the remaining portion (primarily the threaded portions), while only the threaded portions of the pin and the box initially contact, a low friction state is achieved by the lubricating coating having a low coefficient of friction which covers the threaded portions, so Ts becomes low. In the final stage of makeup, when the seal portions and the shoulder portions start to contact, the high-friction solid lubricating coatings which cover these portions contact, causing a high-friction state to occur and causing Ty to increase. As a result, ΔT is increased.
The present invention, which is based on this knowledge, is a tubular threaded joint constituted by a pin and a box each having a contact surface comprising an unthreaded metal contact portion including a seal portion and a shoulder portion and a threaded portion, characterized in that the contact surface of at least one of the pin and the box has a first lubricating coating and a second lubricating coating, the first lubricating coating being a solid lubricating coating faulted on a portion of the contact surface including the shoulder portion, the second lubricating coating being selected from a viscous liquid lubricating coating and a solid lubricating coating and formed on at least the portion of the contact surface where the first lubricating coating is not present, the first lubricating coating having a coefficient of friction which is higher than that of the second lubricating coating, the second lubricating coating being positioned on top in a portion where both the first lubricating coating and the second lubricating coating are present.
The portion of the contact surface having the first lubricating coating may be just the shoulder portion, but preferably it is the entirety of the unthreaded metal contact portion, namely, the seal portion and the shoulder portion.
The second lubricating coating may be provided just on the portion of the contact surface which does not have the first lubricating coating, or it may be provided on the entire contact surface having the first lubricating coating. In the latter case, the second lubricating coating is positioned on top of the first lubricating coating.
Preferred coating thicknesses of each coating are as follows.
The coating thickness of the first lubricating coating is 5-40 μm.
The coating thickness of the viscous liquid lubricating coating as a second lubricating coating is 5-200 μm. However, when this viscous liquid lubricating coating is positioned on top of the first lubricating coating, the total of the coating thickness of the first lubricating coating and that of the viscous liquid lubricating coating is at most 200 μm.
The coating thickness of the solid lubricating coating as a second lubricating coating is 5-150 μm. However, when this solid lubricating coating is positioned on top of the first lubricating coating, the total of the coating thickness of the first lubricating coating and that of the second solid lubricating coating is at most 150 μm.
When the contact surface of only one of the pin and the box has the first lubricating coating and the second lubricating coating as described above, there are no particular limitations concerning the contact surface of the other member of the pin and the box, and it may be in an untreated state (for example, it may be in a state after the below-described preparatory surface treatment). Preferably, however, at least a portion of the contact surface of the other member and preferably the entirety of the contact surface has any of the following surface treatment coatings formed thereon:
1) a lubricating coating selected from a viscous liquid lubricating coating and a solid lubricating coating,
2) a solid anticorrosive coating, or
3) a lower layer in the form of a lubricating coating selected from a viscous liquid lubricating coating and a solid lubricating coating, and an upper layer in the form of a solid anticorrosive coating.
The solid anticorrosive coating is preferably a coating based on an ultraviolet curing resin. The lubricating coating may be either the above-described first lubricating coating or the second solid lubricating coating.
The contact surface of at least one and preferably both of the pin and the box can be previously subjected to surface treatment by a method selected from one or more of blasting treatment, pickling, phosphate chemical conversion treatment, oxalate chemical conversion treatment, borate chemical conversion treatment, electroplating, and impact plating in order to increase the adhesion and the retention of a coating formed atop the contact surface and/or to increase the galling resistance of the threaded joint.
In a tubular threaded joint according to the present invention, a lubricating coating which is formed on its contact surfaces exhibits a large ΔT as observed with a coating made of a conventional lubricating grease such as compound grease which contains harmful heavy metals. Therefore, even at the time of makeup with a high torque, it is possible to perform makeup without the occurrence of yielding or galling of the shoulder portions. In addition, galling can be suppressed even under severe conditions such as during unstable excavation operations in the sea. Furthermore, since the lubricating coating contains substantially no harmful heavy metals such as lead, it poses almost no burden on the global environment. A tubular threaded joint according to the present invention suppress the occurrence of rust, and it can continue to exhibit a lubricating function even when subjected to repeated makeup and breakout, so it can guarantee gas tightness after makeup.
FIG. 1 schematically shows the unthreaded metal contact portions (the shoulder portions and seal portions) of a special threaded joint.
FIG. 2 is a typical torque chart at the time of makeup of a special threaded joint.
FIG. 3 schematically shows the assembled structure of a steel pipe and a coupling at the time of shipment of the steel pipe.
FIG. 4 schematically shows a cross section of a special threaded joint.
FIGS. 5(A)-5(C) show examples of the structure of coatings on a tubular threaded joint according to the present invention.
FIGS. 6(A)-6(C) show examples of the structure of different coatings on a tubular threaded joint according to the present invention.
Below, embodiments of a tubular threaded joint according to the present invention will be explained in detail by way of example. The present invention is not limited to the below-mentioned embodiments.
FIG. 3 schematically shows the state of a typical tubular threaded joint at the time of shipment. A pin 1 having a male threaded portion 3 a is formed on the outer surface of both ends of a steel pipe A, and a box 2 having a female threaded portion 3 b is formed on the inner surface of both sides of a coupling B. The coupling B is previously connected to one end of the steel pipe A. Although not shown in the drawing, a protector for protecting the threaded portions is previously mounted on the unconnected pin of the steel pipe A and the unconnected box of the coupling B before shipment. These protectors are removed from the threaded joint before use.
As shown in the drawing, in a typical tubular threaded joint, a pin is formed on the outer surface of both ends of a steel pipe and a box is formed on the inner surface of a coupling, which is a separate member. There are also integral tubular threaded joints which do not utilize a coupling and in which one end of a steel pipe is made a pin and the other end is made a box. A tubular threaded joint according to the present invention can be of either type.
FIG. 4 schematically shows the structure of a special threaded joint (referred to below simply as a threaded joint), which is a typical tubular threaded joint used for connecting oil country tubular goods. This threaded joint is constituted by a pin 1 formed on the outer surface of an end of a steel pipe A and a box 2 formed on the inner surface of a coupling B. The pin 1 has a male threaded portion 3 a , a seal portion 4 a located near the tip of the steel pipe, and a shoulder portion 5 a at its end surface. Correspondingly, the box 2 has a female threaded portion 3 b , and a seal portion 4 b and a shoulder portion 5 b on its inner side.
The seal portions and the shoulder portions of the pin 1 and the box 2 are unthreaded metal contact portions, and the unthreaded metal contact portions (namely, the seal portions and the shoulder portions) and the threaded portions are the contact surfaces of the threaded joint. These contact surfaces need to have galling resistance, gas tightness, and rust-preventing properties. In the past, to provide these properties, (a) a compound grease containing heavy metal powder has been applied to the contact surface of at least one of the pin and the box, or (b) a viscous liquid, semisolid, or solid lubricating coating has been formed on the contact surface. However, as stated above, (a) has the problem that it has an adverse effect on humans and the environment, and (b) has the problem of a small ΔT whereby when makeup is carried out with a high torque, there is the possibility of yielding of the shoulder portions occurring before completion of makeup.
A threaded joint according to the present invention has a first lubricating coating and a second lubricating coating on the contact surface of at least one member of the pin and the box. The first lubricating coating is a solid lubricating coating formed on a portion of the contact surface including at least the shoulder portion. The second lubricating coating is selected from a viscous liquid lubricating coating and a solid lubricating coating and formed on at least the portion of the contact surface where the first lubricating coating is not present. The first lubricating coating is a coating having relatively high friction with a coefficient of friction which is higher than the coefficient of friction of the second lubricating coating.
Below, the first lubricating coating will be referred to as a high-friction solid lubricating coating, and when the second lubricating coating is a solid lubricating coating, that solid lubricating coating will sometimes be referred to as a second solid lubricating coating.
In the locations close to the threaded portions between the threaded portions and the seal portions of the pin and the box of a threaded joint, a portion where the pin and the box do not contact each other when the threaded joint is made up is provided with the object of preventing lubricating components from oozing out at the time of makeup of the threaded joint. In some threaded joints, a non-contacting region where the pin and the box intentionally do not contact is provided. Such portions where the pin and the box do not contact each other at the time of makeup are not part of the contact surfaces, and it does not matter whether a coating according to the present invention is applied to these portions.
A high-friction solid lubricating coating which is the first lubricating coating is formed on just a portion of the contact surface of one or both of the pin and the box which includes the shoulder portion. The portion of the contact surface having the high-friction solid lubricating coating may be just the shoulder portion, but preferably it is the entire unthreaded metal contact portion including the seal portion and the shoulder portion. Namely, the high-friction solid lubricating coating is preferably formed on the seal portion and the shoulder portion of the contact surface of at least one of the pin and the box. At least the remaining portion of the contact surface which does not have the high-friction solid lubricating coating has a second lubricating coating selected from a viscous liquid lubricating coating and a solid lubricating coating formed thereon. The second lubricating coating may be formed on the entire contact surface, in which case the second lubricating coating is positioned on top of the high-friction solid lubricating coating (namely, it forms an upper layer). It is also possible for the second lubricating coating to be formed just on the portion where the high-friction solid lubricating coating is not present (e.g., just on the threaded portion).
When the contact surface of only one member of the pin and the box has the high-friction solid lubricating coating and the second lubricating coating, there is no particular limitation on surface treatment of the contact surface of the other member of the pin and the box. For example, a high-friction solid lubricating coating which may be the same as or different from the first lubricating coating, a viscous liquid lubricating coating or a solid lubricating coating which may be the same as or different from the second lubricating coating, a solid anticorrosive coating, and a combination of a lower layer in the form of a lubricating coating and particularly a viscous liquid lubricating coating and an upper layer in the form of a solid anticorrosive coating can be formed on at least a portion of the contact surface and preferably on the entire contact surface of the other member. Alternatively, the contact surface of the other member can be left untreated, or it can be subjected to just the below-described preparatory surface treatment for surface roughening (such as phosphate chemical conversion treatment).
FIGS. 5(A) -(C) and FIGS. 6(A) -(B) show various possible embodiments of combinations of the first and second lubricating coatings. In these figures, of the male threads of the threaded portion of the pin 1 , the thread 3 a ′ at the extreme end and closest to the seal portion 4 a are formed with an incomplete shape which is observed at the start of thread cutting. By making the thread at the extreme end of the pin incomplete threads, stabbing of the pin becomes easier, and the possibility of damage to the threaded portion of the box at the time of stabbing of the pin is decreased.
FIG. 5(A) shows an embodiment in which the unthreaded metal contact portions (the seal portions and the shoulder portions) of the contact surfaces of both the pin and the box have a high-friction solid lubricating coating 10 , and the remainder of each contact surface, which is primarily the threaded portion, has a second lubricating coating 11 .
FIG. 5(B) shows an embodiment in which the unthreaded metal contact portions of the contact surfaces of both the pin and the box have a high-friction solid lubricating coating 10 , and a second lubricating coating 11 which covers the entirety each contact surface is formed atop each high-friction solid lubricating coating 10 .
FIG. 5(C) shows an embodiment in which one of the pin and the box (the pin in the figure) has a high-friction solid lubricating coating 10 which covers the unthreaded metal contact portion and atop it a second lubricating coating 11 which covers the entire contact surface in the same manner as in FIG. 5(B) , and the entire contact surface of the other member (the box in the figure) is coated with a second lubricating coating 11 .
FIG. 6(A) shows an embodiment in which one of the pin and the box (the pin in the figure) has a high-friction solid lubricating coating which covers the to unthreaded metal contact portion and a second lubricating coating 11 which covers the remainder of the contact surface in the same manner as in FIG. 5(A) , and the entire contact surface of the other member (the box in the figure) is covered by a second lubricating coating 11 .
FIG. 6(B) shows an embodiment in which one of the pin and the box (the box in the figure) has a high-friction solid lubricating coating 10 which covers the unthreaded metal contact portion and a second lubricating coating 11 which covers the remainder of the contact surface in the same manner as in FIG. 5(A) , and the entire contact surface of the other member (the pin in the figure) is covered by a solid anticorrosive coating 12 .
FIG. 6(C) shows an embodiment in which one of the pin and the box (the pin in the figure) has a high-friction solid lubricating coating 10 which covers the unthreaded metal contact portions and atop it a second lubricating coating 11 which covers the entire contact surface in the same manner as in FIG. 5(B) , and the entire contact surface of the other member (the box in the figure) is covered by a high-friction solid lubricating coating 10 .
It is understood by those skilled in the art that a tubular threaded joint according to the present invention can have a coating structure which is a combination of coatings other than the combinations described above. For example, the second lubricating coating 11 on one of the pin and the box in FIG. 5(A) or on the pin in FIG. 6(A) can be replaced by a solid anticorrosive coating. In this case, the second lubricating coating 11 which is present on only one member covers the portion on which the high-friction solid lubricating coating is not formed including at least the threaded portion as shown in FIG. 6(B) .
Next, various coatings which cover the contact surfaces of a tubular threaded joint according to the present invention will be explained. Unless otherwise specified, % with respect to the content of components of the coatings means mass %. This content is substantially the same as the content based on the total solids content (the total content of nonvolatile components) of a coating composition for forming a lubricating coating.
[High-Friction Solid Lubricating Coating]
The high-friction solid lubricating coating is a solid lubricating coating having a relatively high coefficient of friction compared to the second lubricating coating. It produces a high-friction state in the final stage of makeup of a threaded joint (starting when the shoulder portions of the pin and the box contact until the seal portions intimately contact with a predetermined amount of interference), thereby increasing ΔT by increasing Ty and making it difficult for yielding of the shoulder portions to take place even when makeup is carried out with a high torque.
In the present invention, a high-friction solid lubricating coating which has such an effect is provided so as to cover a portion of the contact surface including at least the shoulder portion of at least one of a pin and a box. Preferably, the entirety of the unthreaded metal contact portion including the seal portion and the shoulder portion is covered by the high-friction solid lubricating coating. When a threaded joint has a plurality of seal portions and shoulder portions, it is preferable to cover the entirety of the seal portions and the shoulder portions with a high-friction solid lubricating coating. However, the objective of increasing ΔT can be achieved even if only the shoulder portions where contact initially takes place in the final stage of makeup of a threaded joint are covered with a high-friction solid lubricating coating. The location where a high-friction solid lubricating coating is formed can be suitably set in accordance with the shape of a joint and the required performance.
Even when a second lubricating coating 11 is formed atop the high-friction solid lubricating coating 10 such as on the pin 1 and the box 2 as shown in FIG. 5(B) or on the pin 1 as shown in FIG. 5(C) , a high-friction state is achieved by the high-friction solid lubricating coating 10 in the final stage of makeup, and a desired effect of increasing ΔT can be achieved. The high-friction solid lubricating coating needs to have a higher coefficient of friction than the second lubricating coating 11 . A certain degree of adhesion to the substrate (the contact surfaces of the pin and the box, which may be in an as-machined state or may have a preparatory surface treatment coating such as one formed by phosphate chemical conversion treatment or metal plating) is necessary.
An example of a high-friction solid lubricating coating which is suitable for use in the present invention is a coating comprising an organic resin or inorganic polymer which contains little or no solid lubricating particles (such as in an amount of at most 5 mass %, preferably at most 3 mass %, and more preferably at most 1 mass % based on the total solids content).
A particularly preferred high-friction solid lubricating coating is a solid lubricating coating which is formed from a film-forming composition which is used for lubricating treatment before hydroforming of steel. Specific examples of such a composition are Surflube C291 manufactured by Nippon Paint Co., Ltd. (based on a water-soluble resin) and Gardolube L6334 and L6337 manufactured by Chemetall GmbH. A solid lubricating coating formed from this type of composition has a higher coefficient of friction than a lubricating coating used for lubricating threaded joints (such as a lubricating coating selected from a viscous liquid lubricating coating and a second solid lubricating coating used in the present invention), and it forms a solid lubricating coating having good adhesion and affinity to a lubricating coating. However, the solid lubricating coating which is formed still has good lubricating properties and sliding properties, so as shown in FIG. 5(A) and FIG. 6(B) , for example, even if a second lubricating coating having a low coefficient of friction is not present on the unthreaded metal contact portion including the shoulder portion, galling resistance necessary for makeup and sufficient gas tightness after makeup are obtained if a second lubricating coating is present on the threaded portions of at least one of the pin and the box.
Another high-friction solid lubricating coating which can be used is a coating comprising the same components as the below-described second solid lubricating coating but which has a reduced content of a solid lubricant (lubricating powder).
The coefficient of friction of a solid lubricating coating or a viscous liquid lubricating coating can be measured in accordance with ASTM D2625 (load carrying capacity and lifespan of solid film lubricants) or ASTM D2670 (wear properties of fluid lubricants) by the Falex pin and Vee block method (referred to below as the Falex method) using a Falex pin and Vee block machine. In the Falex method, blocks (Vee blocks) having a tip with a V-shaped opening are disposed facing opposite sides of a pin, and the pin is rotated while applying a predetermined pressure loading to the blocks to measure the coefficient of friction.
Measurement of the coefficient of friction can be carried out using test pieces constituted by blocks and a pin which are taken from a steel billet made of the same material as used in a tubular threaded joint and which have undergone the same preparatory surface treatment and surface coating treatment. Measurement is carried out at around 1 GPa, which corresponds to the maximum pressure of the seal portions at the time of makeup of a tubular threaded joint, and the average coefficient of friction in a steady frictional state before the occurrence of galling can be compared. Of course, a high-friction solid lubricating coating according to the present invention can be selected based on the coefficient of friction measured using another friction measuring apparatus normally used in a laboratory. Whatever the measurement method, it is sufficient for the coefficient of friction of the high-friction solid lubricating coating to be higher than the coefficient of friction of the second lubricating coating when measurement is carried out under the same conditions.
As long as the high-friction solid lubricating coating according to the present invention has a higher coefficient of friction than the viscous liquid lubricating coating or the second solid lubricating coating used as the second lubricating coating, there is no particular lower limit on the coefficient of friction of the high-friction solid lubricating coating. However, in order to adequately achieve the objective of increasing Ty and increasing ΔT, the coefficient of friction of the high-friction solid lubricating coating is preferably larger by a certain extent than the coefficient of friction of the second lubricating coating. Preferably, the coefficient of friction of the high-friction solid lubricating coating is at least 1.5 times, more preferably at least 2 times, and most preferably at least 2.5 times the coefficient of friction of the second lubricating coating.
The coefficient of friction of the high-friction solid lubricating coating as measured by the above-stated Falex method is preferably at least 0.06, more preferably at least 0.08, and most preferably at least 0.1. Since an extremely high coefficient of friction has an adverse effect on the galling resistance of a threaded joint, the coefficient of friction of the high-friction solid lubricating coating is preferably at most 0.25 and more preferably at most 0.20.
The thickness of the high-friction solid lubricating coating is preferably 5-40 μm. If it is less than 5 μm, the effect of producing a high level of friction at the time of contact and galling resistance may be inadequate. On the other hand, if it exceeds 40 μm, not only does the friction-increasing effect reach a limit but an adverse effect on the properties of the seal portion may develop.
The high-friction solid lubricating coating can be formed by coating methods well known to those skilled in the art. In order to form a high-friction solid lubricating coating on a portion of the contact surface of the pin and/or the box, namely, on only the shoulder portion or on the unthreaded metal contact portion including the seal portion and the shoulder portion, spray coating can be carried out while shielding with a suitable means the portions where it is not desired to form the high-friction solid lubricating coating. Upon drying to evaporate solvents after application, a high-friction solid lubricating coating is formed.
[Viscous Liquid Lubricating Coating]
A viscous liquid lubricating coating can be formed using a lubricating grease which has been conventionally used to improve the galling resistance of the contact surfaces of a threaded joint. It is preferable to use a lubricating grease referred to as green dope which has little adverse effect on the environment and contains no or little heavy metal powder.
A preferred example of such a viscous liquid lubricating coating is a coating comprising a suitable amount of a base oil and at least one material selected from a rosin-based material, wax, metal soap, and a basic metal salt of an aromatic organic acid. Of these components, a rosin-based material is effective primarily at increasing the coefficient of friction of a lubricating coating, namely, at increasing ΔT, while wax, metal soap, and a basic metal salt of an aromatic organic acid are effective primarily at preventing galling of a lubricating coating. Therefore, it is possible for a coating to exhibit adequate lubricating performance even if it does not contain a powder of a soft heavy metal such as lead or zinc. A particularly preferable viscous liquid lubricating coating comprises all of a rosin-based material, wax, metal soap, and a basic metal salt of an aromatic organic acid.
A rosin-based material is selected from rosin and its derivatives. When it is contained in a lubricating coating, it becomes highly viscous when it undergoes a high pressure in a frictional interface. As a result, it is effective at increasing ΔT of the coating. The rosin which is used may be any of tall rosin, gum rosin, and wood rosin, and various rosin derivatives such as rosin esters, hydrogenated rosins, polymerized rosins, and disproportionated rosins can also be used. The content of the rosin-based material in the lubricating coating is preferably 5-30% and more preferably 5-20%.
The description continues in the full USPTO document.
About 6,653 words. The USPTO PDF has it with every drawing.
Fees are due 3.5, 7.5 and 11.5 years after grant. This patent expired on September 5, 2025, so the fee marked "not paid" was the one that went unpaid.
TUBULAR THREADED JOINT HAVING IMPROVED HIGH TORQUE PERFORMANCE
Filed Nov 2012 · published Sep 2014Tubular threaded joint having improved high torque performance
Filed Nov 2012 · granted Sep 2017Earlier publications, parents and continuations. None of them can still be enforced, or this patent would not be listed.
Prior art cited by the examiner or applicant. Useful when you check your own idea for novelty.
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